PROJECT SUMMARY/ABSTRACT Physical activity (PA) is one of the best predictors of sustained weight loss and current guidelines recommend high levels of PA to prevent weight regain after weight loss. However, long-term adherence to PA is generally poor when adults with overweight/obesity are provided an exercise prescription consistent with current guidelines. Thus, it is essential to evaluate novel strategies to enhance adoption and maintenance of PA in adults with overweight/obesity. The overall goal of this mentored F32 application is to use mixed methods research to optimize an innovative, theoretically based PA intervention designed to enhance motivation for exercise in adults with overweight/obesity. Specifically, quantitative data (Aim 1) will be integrated with qualitative data (Aim 2) to optimize an intervention designed to enhance MOtiVation for Exercise (MOVE) in adults with overweight/obesity (Aim 3). In Aim 1, a latent transition analysis will be used to examine longitudinal measures of motivation for exercise and objective PA data collected in 170 adults enrolled in a recently completed behavioral weight loss trial (R01DK097266). In Aim 2, adults from an ongoing behavioral weight loss trial (R01DK111622) will receive the MOVE intervention and participate in focus groups to explore how participants experience MOVE. In Aim 3, quantitative and qualitative results will be integrated to optimize MOVE. The applicant, Dr. Danielle Ostendorf, received graduate training in chronic disease epidemiology, clinical trial management, and person-centered analytical approaches including latent profile analysis. Dr. Ostendorf?s long-term goal is to develop an independent research program that focuses on the prevention and treatment of chronic diseases, including obesity, by improving strategies to increase PA. To build upon her graduate training and expand her scientific skillset, Dr. Ostendorf and her mentorship team have developed a comprehensive training plan. Dr. Ostendorf?s primary training objectives include obtaining training in: (1) additional direct clinical research experience, (2) behavior change theory and strategies, (3) latent transition analysis, a longitudinal extension of latent profile analysis, (4) qualitative data analysis and mixed methods research, and (5) strengthening granstmanship, publishing, and professional development skills. This research and training will take place at the University of Colorado Anschutz Medical Campus, an exceptional environment that offers endless world-class opportunities for Dr. Ostendorf to gain valuable skills and experiences that will foster her development as an independent researcher. Successful completion of this proposal will result in several first-authored publications and will generate critical preliminary data needed to support a competitive K01 application. This F32 proposal, with its focus on expanding Dr. Ostendorf?s expertise in advanced statistical methods and development of new research skills in mixed methods approaches, will serve as both a superb training opportunity and as an original and meaningful scientific contribution to propel Dr. Ostendorf?s career forward as an independent investigator.